There are many applications for which precise control over the amount and/or rate at which a fluid is dispensed by a dispensing apparatus is necessary. In semiconductor processing, for example, it is important to control the amount and rate at which photochemicals, such as photoresist chemicals, are applied to a semiconductor wafer. The coatings applied to semiconductor wafers during processing typically require a uniformity of thickness across the surface of the wafer that is measured in angstroms. The rates at which processing chemicals are applied to the wafer must be controlled in order to ensure that the processing liquid is applied uniformly.
Many photochemicals used in the semiconductor industry today are very expensive, frequently costing upwards of $1000 a liter. Therefore, it is preferable to ensure that chemical processing equipment is operating correctly. Additionally, it is desirable to reduce the cycle time for dispensing fluid on a wafer.
Many current photochemical dispense systems utilize filters to remove impurities from the process fluid. In such systems, the filter must be primed to fully wet the filter and multiple dispenses performed to flush all the air out of the filter before the pump is ready for production dispenses. It can take hours of dispense cycles before the pump is ready. Each non-production dispense cycle that occurs leads to wasted fluid and machine time.